Add doxygen description for the chrono::vehicle namespace
Add doxygen description for the chrono::vehicle namespace

dariomangoni/chrono,armanpazouki/chrono,armanpazouki/chrono,Bryan-Peterson/chrono,projectchrono/chrono,Milad-Rakhsha/chrono,Milad-Rakhsha/chrono,dariomangoni/chrono,armanpazouki/chrono,jcmadsen/chrono,jcmadsen/chrono,jcmadsen/chrono,Bryan-Peterson/chrono,projectchrono/chrono,amelmquist/chrono,Milad-Rakhsha/chrono,jcmadsen/chrono,tjolsen/chrono,tjolsen/chrono,rserban/chrono,Bryan-Peterson/chrono,dariomangoni/chrono,armanpazouki/chrono,andrewseidl/chrono,andrewseidl/chrono,Milad-Rakhsha/chrono,projectchrono/chrono,dariomangoni/chrono,jcmadsen/chrono,dariomangoni/chrono,amelmquist/chrono,armanpazouki/chrono,tjolsen/chrono,dariomangoni/chrono,rserban/chrono,projectchrono/chrono,amelmquist/chrono,andrewseidl/chrono,projectchrono/chrono,Bryan-Peterson/chrono,amelmquist/chrono,Bryan-Peterson/chrono,rserban/chrono,Milad-Rakhsha/chrono,Milad-Rakhsha/chrono,armanpazouki/chrono,rserban/chrono,andrewseidl/chrono,andrewseidl/chrono,jcmadsen/chrono,jcmadsen/chrono,amelmquist/chrono,amelmquist/chrono,rserban/chrono,tjolsen/chrono,projectchrono/chrono,tjolsen/chrono,rserban/chrono,rserban/chrono